The diamond monopoly is over, writes Paul Zimnisky in his study of worldwide diamond industry, but he wonders how concentrated the industry remains: For the majority of the 20th century the diamond industry was conspicuously controlled De Beers, hoarding of over 80% of the worlds rough diamond supply in an attempt to manage global supply and thus prices.
However, a series of events over the last two-and-a-half decades reduced De Beers controlling share to 35%. In a monopoly one seller dominates the entire market. In an oligopoly a small number of large sellers dominate the market. While an oligopoly does consists of multiple players, the sellers can still individually set production quantities and prices and significantly influence the market...............................................Full Article: Source